It is desirable to determine the presence of objects, such as contraband, weapons, or explosives, that have been concealed, for example, in a moving vehicle, or on a person, or in any inspected object, while the inspected object is moved past one or more systems that image the contents of the object using penetrating radiation. The determination should be capable of being made while the inspected object is in motion, or, alternatively, while the inspection system is in motion with respect to the inspected person or object. Indeed, since inspection rate, and thus hourly throughput, is at a premium, it is desirable that the vehicle, for example, be driven without requiring the driver or passengers to alight. In case a detection is made, a visual image should be available for verification.
The use of images produced by detection and analysis of penetrating radiation scattered from an irradiated object, container, or vehicle is the subject, for example, of U.S. Pat. No. 6,459,764, to Chalmers et al. (the “Chalmers patent”), issued Oct. 1, 2002, and incorporated herein by reference. The Chalmers patent teaches backscatter inspection of a moving vehicle by illuminating the vehicle with x-rays from above or beneath the moving vehicle, as well as from the side.
The use of an x-ray source and an x-ray detector, both located in a portal, for purposes of screening personnel, is the subject, for example, of U.S. Pat. No. 6,094,472, to Smith, issued Jul. 25, 2000.
X-rays are scattered from matter in all directions, therefore, scatter may be detected by an x-ray detector disposed at any angle to the scattering material with respect to the direction of incidence of the illuminating radiation. Therefore, a “flying spot” irradiation system is typically used, whereby a single point on the inspected object is illuminated with penetrating radiation at any given moment, so that the locus of scatter can be determined unambiguously, at least with respect to the plane transverse to the direction of the beam of penetrating radiation.
In order to obtain multiple views of an inspected object, multiple backscatter imaging systems may be employed in a single inspection tunnel. This may result in interference, or cross-talk, between respective imaging systems, resulting in image degradation. This is due to the lack of each flying-spot imager's ability to distinguish the origin of the scattered radiation from each imager's source. To date, this problem has been addressed by placing the imagers some distance apart to minimize cross talk. This approach causes the size of the overall system to increase. In space-limited applications, this is often undesirable.